Rahman Md Khalidur, Yamada Takeshi, Yamada Norifumi L, Hishida Mafumi, Higuchi Yuji, Seto Hideki
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Naka, Ibaraki 319-1106, Japan.
Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
Struct Dyn. 2023 Aug 21;10(4):044701. doi: 10.1063/4.0000184. eCollection 2023 Jul.
The dynamics of hydration water (HW) in 1,2-dimyristoyl--glycero-3-phosphoethanolamine (DMPE) was investigated by means of quasi-elastic neutron scattering (QENS) and compared with those observed in 1,2-dimyristoyl--glycero-3-phosphocholine (DMPC). The headgroup dynamics of DMPE was investigated using a mixture of tail-deuterated DMPE and DO, and the QENS profiles were interpreted as consisting of three modes. The fast mode comprised the rotation of hydrogen atoms in -NH and -CH- groups in the headgroup of DMPE, the medium-speed mode comprised fluctuations in the entire DMPE molecule, and the slow mode comprised fluctuations in the membrane. These interpretations were confirmed using molecular dynamics (MD) simulations. The HW dynamics analysis was performed on a tail-deuterated DMPE and HO mixture. The QENS profiles were analyzed in terms of three modes: (1) a slow mode, identified as loosely bound HW in the DMPC membrane; (2) a medium-speed mode similar to free HW in the DMPC membrane; and (3) a fast mode, identified as rotational motion. The relaxation time for the fast mode was approximately six times shorter than that of rotational water in DMPC, consistent with the results of terahertz time-domain spectroscopy. The activation energy of medium-speed HW in DMPE differed from that of free HW in DMPC, suggesting the presence of different hydration states or hydrogen-bonded networks around the phosphocholine and phosphoethanolamine headgroups.
通过准弹性中子散射（QENS）研究了1,2-二肉豆蔻酰-sn-甘油-3-磷酸乙醇胺（DMPE）中水合水（HW）的动力学，并与在1,2-二肉豆蔻酰-sn-甘油-3-磷酸胆碱（DMPC）中观察到的动力学进行了比较。使用尾部氘代的DMPE和D₂O的混合物研究了DMPE的头部基团动力学，并且QENS谱被解释为由三种模式组成。快速模式包括DMPE头部基团中-NH和-CH-基团中氢原子的旋转，中速模式包括整个DMPE分子的波动，而慢速模式包括膜中的波动。使用分子动力学（MD）模拟证实了这些解释。对尾部氘代的DMPE和H₂O的混合物进行了HW动力学分析。根据三种模式分析了QENS谱：（1）慢速模式，被确定为DMPC膜中松散结合的HW；（2）类似于DMPC膜中自由HW的中速模式；（3）快速模式，被确定为旋转运动。快速模式的弛豫时间比DMPC中旋转水的弛豫时间短约六倍，这与太赫兹时域光谱的结果一致。DMPE中速HW的活化能与DMPC中自由HW的活化能不同，这表明在磷酸胆碱和磷酸乙醇胺头部基团周围存在不同的水合状态或氢键网络。
